Have you Equalized your FOX Float EVOL Air Sleeve? (rear shock)

[GrandPaBrogan]

Pertains to the Fox Float DPS Performance model / 3 position lever / Trunnion mount
Stock standard on Giant Trance e+3Pro and e+2Pro. (Not sure if this applies to other shock units with external piggyback cylinders)

Giant provides a pretty feeble owners manual - with nothing about the air shocks they come equipped with. I guess it's up to the LBS (or the owner) to sort that out. When I got my bike new, the front fork pressure was too high and the rear shock was too low. I know how to set-up correct pressures by measuring sag to 25%-30% so that's what I did - that's how it's been for a couple of months.

My rear shock did feel stiff though and ramps up too quick for my liking. I just assumed that was the way the Maestro linkage worked. I was about to see if Fox rear shocks have internal tokens so I could increase the positive air chamber volume (to free up the mid stroke). So I looked-up details and specs for my shock for the very first time... duh.

Here's what I discovered:

When adding air to the air chamber, it is important to equalize the positive and negative air chambers by slowly compressing the shock through 25% of its travel 10-20 times after every 50psi addition.

• Adding air to the shock without periodically equalizing the air chambers can lead to a condition in which the shock has more pressure in the positive chamber than the negative. In this condition the shock will be very stiff and can top-out. You can equalize the air chambers by slowly compressing the shock until you feel and hear a transfer of air. Hold the shock at this point for a few seconds to allow the air to transfer from the positive to the negative chamber.

When releasing air from the air chamber, it is important to do this slowly so the shock can transfer air from the negative to positive chamber and then be realeased through the Schrader valve.

• Releasing the air pressure too quickly can induce a condition in which the negative chamber has more pressure than the positive chamber. In this condition the shock will compress into its travel and not fully extend. You can remedy this by adding air pressure until the shock extends, then slowly compressing the shock through 25% of its travel 10-20 times.

As it transpired on new bike day, I wanted to see how far down I could move the O-ring sag marker so I took more air out of the shock (to less than 100psi) until it bottomed-out when I sat on it. I wanted to see the true shock stroke length. Then I pumped it all the way up (240psi) and let air out a little bit at a time until I got the sag I wanted. Without knowing that I needed to do progressive equalisation as the manual says, I inadvertently stuffed-up the EVOL pressure balance.

Just to be extra sure, I took the pressure back down to under 100 psi then equalised every 30psi increments instead of the recommended 50psi. Sitting on the bike, I did feel the transfer of air and sat there for moment before pumping up again. When I connected the pump each time, I noticed that there was a pressure drop from the previous - so I guess the air pressure gets sucked into the negative chamber.

What a difference! The shock is plusher than I ever remember it to be. Bumps don't feel as harsh anymore. I've also gained more stroke distance - the O-ring is now further down near the end. I no longer need to play around with air-reducer tokens (which as it turned out, are also available if needed).

- - -
Further reference:
SHOCK- 2018 FLOAT DPS and DPX2 | Bike Help Center | FOX

 

[tedturbine]

This has come up a few times recently so you are not alone. You may find that your forks benefit from the same approach. I let both ends to 0 on mine then went up 30psi each time

 

[ggx]

bike Setup = rocket science

 

[GrandPaBrogan]

This has come up a few times recently so you are not alone. You may find that your forks benefit from the same approach. I let both ends to 0 on mine then went up 30psi each time

Ah, but of course... this should apply for the fork too (or any shock with an auto negative air spring chamber)!! Thanks for the reminder, somehow this realisation escaped me.

I kinda did the exact same thing to my fork when I removed one of the three internal tokens recently. I pumped it all the way up and released air bit by bit until I got the sag I wanted.

I achieved what I wanted and the fork at mid stroke is now lively and only ramps up nicely at the end of the stroke. But when I first sit on the bike, the fork will sag as it should - but then it will noticeably drop a little bit more. It didn't appear to affect the performance so I left it alone.

I just did what you suggested the shadow sag-drop is gone! I think it changed the mid-stroke characteristic a little bit too... it blows through just as quick and lively - but not as linear as before, I'm guessing because the negative air chamber isn't over charged. That should only be a good thing.

 

[GrandPaBrogan]

bike Setup = rocket science

Ha... and don't even get me started on Tyre set-up!

When I first started mountain biking (cough) there was only one size tyre... 26 x 2.25 and that was the fat one! (The XC crowd used 26 x 1.75 thinking that was faster until it was proven that it wasn't.)

This was even before tubeless, so all we had to choose was the tread pattern and maybe the weight if you're fussy. Tyres these days... crumbs, let's not even go there!

 

[Bryan Wells]

If anyone on here needs a real through explanation of how your suspension works, myths, truths etc. feel free to tag me. I own "Infinity Cyclery" out of Washington and I specialize in suspension work. I have been deep into the shock shown above more than I can count lol. Cheers guys!

 

[DrStupid]

I'm confused. Wouldn't it just equalized as soon as you started riding?

 

[GrandPaBrogan]

I'm confused. Wouldn't it just equalized as soon as you started riding?

That’s how I expected it to work too. The air shocks and forks I had used 10 years ago (various Rockshox and Mainitou) didn’t need to be primed in this way that I’m aware of. The new systems must have some sort of gate.

Might pay to tag Mr Wells to shed more light about the subject.

 

[steve_sordy]

I suspect that a lot of bike techs in bike shops all over the world are unaware that they now need to equalise suspension. They are guilty of not keeping up to date. We punters can be given a small excuse as we don't buy new bikes that often, but those guys not only do it for a living, but are exposed to industry stuff on a regular basis.

 

[DrStupid]

Ok.. so based on the instructions. If you change pressure by more than 50 psi... sit on the bike for 20 seconds to equalise chambers? Either the instructions are lacking some crucial piece of information I need to make the connection, like a bleeder port needing to reached in the stroke to allow balancing between chambers, or I'm just completley lost as to what about this procedure is different from just going for a little ride after changin pressure. Help me understand!

 

[GrandPaBrogan]

Ok.. so based on the instructions. If you change pressure by more than 50 psi... sit on the bike for 20 seconds to equalise chambers?

Nah, before you sit for a moment you need to slowly push through at least 25% of the shock travel - slowly up and down, around 20 times... then sit on it for a moment. Sometimes you can feel or hear the air pressure drop a bit, sometimes you don’t but just carry on.

At first I did this with the pump still connected, but each time I depressed the shock my pressure gauge needle pointer went all over the show, so I removed the pump each interval just in case it was bad for the pump.

I’m guessing there’s a pressure differential valve in between the main positive chamber and the negative chamber. As long as the difference in pressure between the two chambers is less than 50psi the valve can let air equalise (if you depress it up and down - I have no idea why at least 20 times is the magic number to open the valve). If the pressure difference exceeds more than 50psi then the valve will remain closed.

The same thing happens the opposite way I guess - if you let the air out too quickly. The valve shuts off and whatever pressure there is in the negative chamber remains trapped in there - even though you’ve emptied the shock. According to the manual this creates a problem in two ways. 1) the shock won’t extend fully (you’ve effectively decreased your travel) and 2) the shock will bottom out too easily - if the pressure differential is too extreme, should the positive chamber be pumped back up to a lesser amount than the pressure that’s still trapped inside the negative chamber.

I could be wrong but that’s how I understand what takes place.

 

[MinusPrevious]

Will do this prior to my next ride. Thanks for the info!

 

[DrStupid]

Nah, before you sit for a moment you need to slowly push through at least 25% of the shock travel - slowly up and down, around 20 times... then sit on it for a moment. Sometimes you can feel or hear the air pressure drop a bit, sometimes you don’t but just carry on.

At first I did this with the pump still connected, but each time I depressed the shock my pressure gauge needle pointer went all over the show, so I removed the pump each interval just in case it was bad for the pump.

I’m guessing there’s a pressure differential valve in between the main positive chamber and the negative chamber. As long as the difference in pressure between the two chambers is less than 50psi the valve can let air equalise (if you depress it up and down - I have no idea why at least 20 times is the magic number to open the valve). If the pressure difference exceeds more than 50psi then the valve will remain closed.

The same thing happens the opposite way I guess - if you let the air out too quickly. The valve shuts off and whatever pressure there is in the negative chamber remains trapped in there - even though you’ve emptied the shock. According to the manual this creates a problem in two ways. 1) the shock won’t extend fully (you’ve effectively decreased your travel) and 2) the shock will bottom out too easily - if the pressure differential is too extreme, should the positive chamber be pumped back up to a lesser amount than the pressure that’s still trapped inside the negative chamber.

I could be wrong but that’s how I understand what takes place.

This helps a great deal. Thanks for your patience and the information. I generally have two modes... over thinking everything or not thinking at all.

 

[GrandPaBrogan]

Will do this prior to my next ride. Thanks for the info!

If you didn't make any radical pressure adjustments on your shock since new, your rear shock unit (and/or fork) might be OK still. One would think that the shock units would've been equalised properly from the factory. But then again, there's nothing to lose if you want to redo it just to make sure.

This helps a great deal. Thanks for your patience and the information. I generally have two modes... over thinking everything or not thinking at all.

I have three modes... the same two you mentioned, and the third - I'm eating something while thinking about some other food.

 

[GrandPaBrogan]

Hey guys, I gotta say... this is the best thing I've ever discovered and done to my bike!

Just came back from a 20 km ride with my wife in a paved bike path. The thing about my off-road trail rides is that there's a lot happening that masks poor suspension characteristics (unless it's a major issue of course). But a paved bike path run (with smooth bumps and some rapid undulations, off-on-off street transitions) will show minute issues like poor compression and rebound behaviour, if damping is too strong or not enough, etc. Other than your knobby tyre hum and freewheel ratchet, it's quiet so you'd also hear suspension related rattling or clunking sounds if there are any.

Since I've equalised both my rear shock and fork, my suspension is dead silent over bumps! Even when I deliberately run square onto a street curb. The initial movement over bumps is plush... the mid-stroke is lively yet has a firmness to it, no clunks or wobbles.